It is common for an aircraft assembly to include a first body pivotally coupled to a second body. Often, the bodies will be coupled via a pin joint which defines a pivot axis. Examples of such assemblies are landing gear stay arms, lock stays, torque links and the bogie pivot joint.
In order to keep friction at an acceptable level, it is generally a requirement that fresh grease is periodically applied to aircraft assembly joints during maintenance operations; for example, every 500 landing cycles.
Such maintenance operations can be time consuming and costly. Moreover, a joint can become dry in the absence of a required quantity of grease, which can increase wear and friction.